Our main objectives are to elucidate the biochemical and molecular mechanisms involved in the digestion and absorption of dietary proteins and peptides in the intestine. During this grant period, we will investigate the chemical structure of two purified brush border peptidases, i.e. aminopeptidase and dipeptidyl peptidase IV to determine the functional and structural domains of these enzymes in relation to the brush border membrane. In addition, the spatial relationship of these enzymes with other components within the brush border membrane will be investigated using bifunctional cross-linking agents. The mechanisms of biosynthesis, intracellular processing and insertion of these enzymes into the brush border membrane will be determined by using specific antisera, radioimmunoassay and subcellular fractionation methods. Solubilization, purification and subcellular localization of intestinal mucosal aminopeptidases, dipeptidyl peptidases, neutral endopeptidases and proteases will be investigated. The kinetic and physicochemical properties of these enzymes in soluble & membrane bound form and factors affecting their activities will be studied. The effects of diets, hormones and drugs on the activities and turnover of these enzymes in the intestinal mucosal cell will be studied in an effort to examine the regulatory components of the peptidase system. Finally, the substrate specificity, kinetics and number of transport systems for peptides of various compositions and lengths will be investigated.